Python: Find the indices of two numbers that sum to 0 in a given list

Last update on April 17 2025 13:03:04 (UTC/GMT +8 hours)

Indices of Numbers Summing to Zero

Write a Python program to find the indices of two numbers that sum to 0 in a given list of numbers.

Input:
[1, -4, 6, 7, 4]
Output:
[4, 1]

Input:
[1232, -20352, 12547, 12440, 741, 341, 525, 20352, 91, 20]
Output:
[1, 7]

Visual Presentation:

Python: Find the indices of two numbers that sum to 0 in a given list.

Sample Solution-1:

Python Code:

# License: https://bit.ly/3oLErEI

# Define a function named 'test' that takes a list of numbers 'nums' as input
def test(nums):
    # Create a set 's' from the given list 'nums'
    s = set(nums)
    
    # Iterate over each element 'i' in the set 's'
    for i in s:
        # Check if the negation of 'i' is also in the set 's'
        if -i in s:
            # If found, return the indices of 'i' and its negation in the original list 'nums'
            return [nums.index(i), nums.index(-i)]

# Assign a specific list of numbers 'nums' to the variable
nums = [1, -4, 6, 7, 4]

# Print the original list of numbers 'nums'
print("Original List:")
print(nums)

# Print a message indicating the operation to be performed
print("Indices of two numbers that sum to 0 in the said list:")

# Print the result of the test function applied to the 'nums' list
print(test(nums))

# Assign another specific list of numbers 'nums' to the variable
nums = [1232, -20352, 12547, 12440, 741, 341, 525, 20352, 91, 20]

# Print the original list of numbers 'nums'
print("\nOriginal List:")
print(nums)

# Print a message indicating the operation to be performed
print("Indices of two numbers that sum to 0 in the said list:")

# Print the result of the test function applied to the 'nums' list
print(test(nums))

Sample Output:

Original List:
[1, -4, 6, 7, 4]
Indices of two numbers that sum to 0 in the said list:
[4, 1]

Original List:
[1232, -20352, 12547, 12440, 741, 341, 525, 20352, 91, 20]
Indices of two numbers that sum to 0 in the said list:
[1, 7]

Flowchart:

Sample Solution-2:

Python Code:

# License: https://bit.ly/3oLErEI

# Define a function named 'test' that takes a list of numbers 'nums' as input
def test(nums):
    # Initialize an empty list 'result' to store the indices
    result = []

    # Iterate over each index 'ind' in the range of the length of the list 'nums'
    for ind in range(len(nums)):
        # Iterate over each index 'i' in the range of the length of the list 'nums'
        for i in range(len(nums)):
            # Check if the current index 'ind' is not equal to the other index 'i'
            # and if the sum of the numbers at the current index and the other index is zero
            if ind != i and nums[ind] + nums[i] == 0:
                # Append the current index 'ind' and the other index 'i' to the 'result' list
                result.append(ind)
                result.append(i)
                # Found the indices; no need to go through the whole list
                return result

# Assign a specific list of numbers 'nums' to the variable
nums = [1, -4, 6, 7, 4]

# Print the original list of numbers 'nums'
print("Original List:")
print(nums)

# Print a message indicating the operation to be performed
print("Indices of two numbers that sum to 0 in the said list:")

# Print the result of the test function applied to the 'nums' list
print(test(nums))

# Assign another specific list of numbers 'nums' to the variable
nums = [1232, -20352, 12547, 12440, 741, 341, 525, 20352, 91, 20]

# Print the original list of numbers 'nums'
print("\nOriginal List:")
print(nums)

# Print a message indicating the operation to be performed
print("Indices of two numbers that sum to 0 in the said list:")

# Print the result of the test function applied to the 'nums' list
print(test(nums))

Sample Output:

Original List:
[1, -4, 6, 7, 4]
Indices of two numbers that sum to 0 in the said list:
[1, 4]

Original List:
[1232, -20352, 12547, 12440, 741, 341, 525, 20352, 91, 20]
Indices of two numbers that sum to 0 in the said list:
[1, 7]

Flowchart:

For more Practice: Solve these Related Problems:

Write a Python program to find the indices of two numbers in a list that sum to zero using a dictionary for lookup.
Write a Python program to implement a two-pointer technique on a sorted list to detect two numbers whose sum is zero and return their indices.
Write a Python program to search a list for a pair of numbers that add to zero without nested loops.
Write a Python program to return the indices of two numbers summing to zero by iterating once and storing complements in a dictionary.

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Python Code Editor :

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